05000336/LER-2003-004, Reactor Coolant System Pressure Boundary Leakage Event

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Reactor Coolant System Pressure Boundary Leakage Event
ML033460378
Person / Time
Site: Millstone Dominion icon.png
Issue date: 12/03/2003
From: Sarver S
Dominion Nuclear Connecticut
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
B19016 LER 03-004-00
Download: ML033460378 (5)


LER-2003-004, Reactor Coolant System Pressure Boundary Leakage Event
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications

10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition

10 CFR 50.73(a)(2)

10 CFR 50.73(a)(2)(iii)

10 CFR 50.73(a)(2)(x)

10 CFR 50.73(a)(2)(iv)(A), System Actuation

10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor

10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat

10 CFR 50.73(a)(2)(v), Loss of Safety Function

10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown
3362003004R00 - NRC Website

text

Dominion Nuclear Connecticut, Inc.

Dominion Millstone Power Station Rope Ferry Road Waterford, CT 06385 DEC 3 2001 Docket No. 50-336 B19016 RE: 10 CFR 50.73(a)(2)(i)(B)

U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Millstone Power Station, Unit No. 2 Licensee Event Report 2003-004-00 Reactor Coolant System Pressure Boundary Leakage Event This letter forwards Licensee Event Report (LER) 2003-004-00, documenting a condition that was discovered at Millstone Unit No. 2, on October 11, 2003. This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B).

There are no regulatory commitments contained within this letter.

Should you have any questions regarding this submittal, please contact Mr. David W. Dodson at (860) 447-1791, extension 2346.

Very truly yours, DOMINION NUCLEAR ECTICUT, INC.

p(P. Sarver, Director ir Station Operations and Maintenance Attachment (1):

LER 2003-004-00 cc:

H. J. Miller, Region I Administrator R. M. Pulsifer, NRC Project Manager, Millstone Unit No. 2 Millstone Senior Resident Inspector ile-D-a

Docket No. 50-336 B1 9016 Millstone Power Station, Unit No. 2 LER 2003-004-00

NRC FORM 366 U.S. NUCLEAR REGULATORY APPROVED BY OMB NO. 3150-0104 EXPIRES 7-31-2004

, the NRC may not conduct or sponsor, (See reverse for reouired number of diaits/characters for each block) and a person is not required to respond to. the Information collection.

FACIUTY NAME (1)

DOCKET NUMBER (2)

PAGE (3)

Millstone Power Station - Unit 2 05000336 1 OF3 TITLE (4)

Reactor Coolant System Pressure Boundary Leakage Event EVENT DATE (5)

LER NUMBER (6)

REPORT DATE ()

l OTHER FACILITIES INVOLVED (a)

FACILITY NAME DOCKET NUMBER MO DAY YEAR YEAR SEUENTIAL REV MO DAY YEAR 05000 1NUM1BER INO.

MO l

~~~~~~~~~~~~

~ ~~~~~~FACILITY NAME lDOCKET NUMBER 10 11 2003 2003-004-00 12 03 2003 05000 OPERATING THIS REPORT IS SUBMITrrEDPURSUANT TO THREOUIREMENTS OF 10 CFR5: (Check all that apply) (11)

MODE (9) 51_

20.2201(b) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(B) 50.73(a)(2)(Ix)(A)

POWER 020.2201(d)

_ 20.2203(a)(4)

_ 50.73(a)(2)(iii)

_ 50.73(a)(2)(x)

LEVEL (10) 0 20.2203(a)(1) 50.36(c)(1)(i)(A) 50.73(a)(2)(iv)(A) 73.71 (a)(4) 20.2203(a)(2)(i) 50.36(c)(1 )(ii)(A) 50.73(a)(2)(v)(A) 73.71 (a)(5) 20.2203(a)(2)(ii)

= 50.36(c)(2) 50.73(a)(2)(v)(B)

OTHER 20.2203(a)(2)(iii) 50.46(a)(3)(il) 50.73(a)(2)(v)(C)

Specify in Abstract below or 20.2203(a)(2)(iv)

_ 50.73(a)(2)(i)(A)

_ 50.73(a)(2)(v)(D)

In (If more space is required, use additional copies of NRC Form 366A) (17) made the same way with a partial penetration J-groove weld of the Alloy 600 to the vessel [VSL] or pipe. This cracking has been observed at virtually all CE designed plants.

The actual safety significance of the cracking found in these heater sleeves is low. The cracks from PWSCC are very tight and the leakage rate was well below the allowable rate of 1 gpm for unidentified leakage. The situation at Millstone Unit No. 2 is similar to the cracking found at other CE designed NSSSs. The defects at Millstone Unit No. 2 were determined by ultrasonic examination to be axial rather than circumferential, and hence significantly less likely to suffer catastrophic failure. Although most industry experience has identified axial cracking, recent inspections at Palo Verde identified the presence of some circumferentially oriented indications, predominantly in the area of the nozzle sleeve above the pressure boundary region. At Millstone Unit No. 2, the potential worst case situation of a circumferential crack that could result in the complete loss of the penetration would be well below the limiting hole size, less than 3 inch, for a Small Break Loss of Coolant Accident, and is therefore bounded by the current analysis basis.

The leaking heater sleeves have been repaired by the use of Mechanical Nozzle Seal Assemblies (MNSAs). The MNSA is a mechanical device with a mechanical seal that encapsulates the pressurizer heater sleeve to prevent leakage in the event of cracks in the sleeve or J-groove welds due to PWSCC of the Inconel 600 material. The MNSA also acts as a restraint to prevent a heater nozzle from ejecting from the vessel in the event of a complete circumferential failure of the heater sleeve. The MNSA design qualification test runs included simulated partial cracks and complete 360 degree cracks in the nozzles. When installed, the MNSA replaces both the sealing and structural integrity functions of the existing weld. Therefore, for heater nozzles repaired with a MNSA, the pressure boundary moves from the internal heater sleeve weld to the compression seal of the MNSA, external to the pressurizer.

4. Corrective Action

The leaking heater sleeves have been repaired by the use of MNSAs. The use of the MNSAs was approved by the Nuclear Regulatory Commission's Safety Evaluation Report, 'Safety Evaluation of Relief Request RR-89-43, Temporary Installation of Mechanical Nozzle Seal Assemblies on Pressurizer Heater Penetration Nozzles, Millstone Power Station, Unit No. 2," dated October 28, 2003 (Accession No. ML032690807).

Long-term resolution of Alloy 600 PWSCC cracking concerns at Millstone Unit No. 2 is being addressed under the Millstone Corrective Action Program (CR-02-05391 and CR-03-08856).

5. Previous Occurrences

The PWSCC of the Alloy 600 heater sleeves at Millstone Unit No. 2 is similar to the PWSCC that has been found in the pressurizer heater nozzles and Control Element/Rod Drive Mechanisms (CEDM/CRDMs) at various plants (including Millstone Unit No. 2) within the past several years. The materials of construction and the design with partial penetration J-groove welds for the pressurizer heater sleeves are the same as for the CEDM/CRDM and Incore Instrumentation (ICI) nozzles. During refueling outage 2R15, Millstone Unit No. 2 completed an inspection of 100% of the reactor vessel head penetrations, 69 CEDMs, 8 ICIs and the vent line, via ultrasonic and liquid penetrant techniques. Eleven penetrations with shallow cracking below the J-groove weld on the outer diameter of eleven CEDMs were repaired. During 2R14, two heater sleeves were repaired with MNSAs and three CEDMs were repaired using a partial penetration replacement technique.

LER:

50-336/2002-001-00 Energy Industry Identification System (EIIS) codes are identified in the text as [XX].